1. Field of the Invention
The present invention relates to a radio-frequency device to be used in an apparatus using radio-frequency electromagnetic waves such as microwaves or millimeter waves.
2. Description of the Related Art
It is known that a slot provided in a grounding conductor serves as an antenna equivalent to an electric dipole to radiate electromagnetic waves. By virtue of its low posture and simple structure, the slot can be utilized for electromagnetic coupling between multilayer boards, power feed to a radiator, or the like, thus lending itself to, for example, radio-frequency circuits in radio devices for use of communications.
Meanwhile, there has been a prior art in which the slot is used in combination with an existing antenna technique to modify antenna characteristics as shown in, for example, Japanese unexamined patent publication No. 2000-196341 A. The outline of the technique described in this document is explained with reference to FIGS. 19A and 19B.
As shown in FIGS. 19A and 19B, this technique relates to a microstrip patch antenna 701 in which a patch 704 formed of a conductor is placed on one surface of a dielectric substrate 702, a grounding layer 703 similarly formed of a conductor is placed on the other surface, and further a power feed line 705 for electrically connecting the patch 704 and a feeding point 706 to each other are formed. Also in this microstrip patch antenna 701, as shown in FIGS. 19A and 19B, a slot 707, which is a cutout portion, is provided in the grounding layer 703, and the slot 707 is placed asymmetrically with respect to a center of the grounding layer 703 so that the balance of a feedback current is collapsed to generate a current of a common mode with a view to achieving non-directionality and broad frequency band of antenna characteristics. It is noted that FIG. 19A is a schematic plan view of the patch antenna 701, and FIG. 19B is a schematic sectional view taken along the line A1–A2 of the patch antenna 701 of FIG. 19A.